Method for creating an avoidance zone

ABSTRACT

A system for controlling pets utilizes a low power transmitter to create avoidance zones in which one pet wearing an animal control receiver can enter but in which a second pet is deterred from entering.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/528,629, entitled “System for Communicating Control Signals” andfiled on Dec. 10, 2003 the contents of which are hereby incorporated byreference in its entirety for all purposes.

This application is being filed concurrently with related U.S. patentapplications: application Ser. No. 10/829,916 entitled “Method andApparatus for Communicating Control Signals”; application Ser. No.10/830,161 entitled “Method and Apparatus for Communicating an AnimalControl Signal”; application Ser. No. 10/830,174 entitled “Method andApparatus for Varying Animal Correction Signals” all of which are herebyincorporated by reference for all purposes.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH OR DEVELOPMENT

NOT APPLICABLE

REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAMLISTING APPENDIX SUBMITTED ON A COMPACT DISK

NOT APPLICABLE

Various embodiments of the invention relate generally to a system forcontrolling an animal. One particular embodiment relates to a system fortransmitting a low power signal for use in keeping pets out of specificareas.

BACKGROUND

Many pet owners experience a variety of problems inside the home causedby their pets getting into areas that the owner would like to keep themout of. For example, dogs getting into trash cans, cats climbing ontables and both cats and dogs climbing on couches are examples of suchproblems.

To combat this problem, electronic transmitter/collar systems have beenused. Such systems operate by producing an electromagnetic field in aspherical pattern. This requires a significant amount of power in orderto generate a strong enough field. Therefore, this has necessitated thatthe transmitter be an alternating current powered unit that is suppliedfrom a wall outlet.

However, many of the locations that owners desire to keep their pets outof are not necessarily located next to a wall outlet. Therefore, tolocate a transmitter in one of these locations would require that powercords be run across the room from the wall outlet. This is clearly anundesirable solution. For example, couches located in the middle of alarge room or a significant distance from a wall outlet cannot be easilysupplied with A/C power. As another example, keeping dogs from drinkingout of a toilet is difficult to achieve as many bathrooms do not havewall outlets located close to the toilet. In addition, even though walloutlets may be located close to some areas, it is often desirable to usethe wall outlets for other items. For example, there are often walloutlets located close to a bed (which one often desires to keep a petoff of); however, those outlets are preferably used for clock radios andreading lights. Consequently, the A/C powered units are oftentimes veryinconvenient to use.

While in many instances a single transmitter will suffice for protectingan area of the home. In some instances it is desirable to protect alarger area than can be accommodated with a single unit. In thatsituation, it can sometimes be difficult to use more than one unit toprotect the large area. This is due to the fact that the units transmitthe same signal in a spherical pattern. When placed near one another,the signals produced by the transmitters can cancel. When the signalscancel one another, a dead zone is created in which the pet can movefreely. This may be the very place that the pet owner wants to keep thepet from entering. As a result, the effective use of two units close toone another which are transmitting the same signal is sometimesdifficult to achieve.

Another difficulty encountered by pet owners is that not all of theirpets need to be kept away from certain areas. For example, a pet owner'sunruly dog may need to be kept away from the front door in order to keepit from jumping up on guests. However, that same pet owner would likethe pet cat to be able to enter the zone by the front door. With asystem in which the dog's collar and the cat's collar are both triggeredby the transmitter signal, it is not possible to create selective zonesaround the door. Thus, such a system suffers from the fact that itcannot accommodate different avoidance zones for different pets in thesame household.

While many animals are capable of being trained to leave an avoidancezone if they enter one, there are sometimes a few that are not deterredby the correction signal used. For example, in some cases, an increasingintensity of the correction signal has been used to cause the moststubborn of animals to leave an avoidance zone. The intensity can onlybe increased to a maximum intensity—especially for commercially soldsystems that must accommodate a diverse group of animals of differentsizes. Thus, in the past, one had to accept that for those animals thatcould not be deterred by the maximum intensity correction signal thatthe system would not be as useful.

SUMMARY

According to one embodiment of the invention, a system is provided foruse in controlling an animal, comprising providing a digital message forcommunication to a receiver; providing a carrier wave for transmissionto the receiver; transmitting the carrier wave in accordance with thedigital message so as to transmit the carrier wave in accordance witheach occurrence of a first digital signal in the digital message and soas not to transmit the carrier wave in accordance with each occurrenceof a second digital signal in the digital message; powering thetransmission with only battery power.

According to another embodiment of the invention, a system is providedfor use in controlling an animal comprising providing a receiver;receiving a carrier wave signal for use in controlling an animal;determining a digital message from the carrier wave signal whereinreception of the carrier wave corresponds to a first digital signal inthe digital message and non-reception of the carrier wave corresponds toa second digital signal in the digital message and wherein the seconddigital signal is opposite in value to the first digital signal; andutilizing the digital message to transmit a correction signal.

According to still another embodiment of the invention, a system isprovided comprising providing a transmitter; powering the transmitter;providing a message for communication to a receiver, wherein the messageis configured to implement a routine for application of a specificcorrection signal to the animal; transmitting the message to thereceiver at less than about 0.0167 Watts average power.

Another embodiment of the invention comprises configuring a receiver toreceive a signal having a predetermined frequency; detecting a signal;taking a first set of samples of the signal at a plurality of intervalsduring a first time period corresponding to at least one cycle at thefrequency; utilizing the first set of samples to calculate acharacteristic of the signal during the first cycle; taking a second setof samples of the signal at a plurality of intervals during a subsequenttime period corresponding to at least one cycle at the frequency;utilizing the second set of samples to calculate the characteristic ofthe signal during the second cycle; comparing the calculatedcharacteristic of the first time period with the calculatedcharacteristic of the subsequent time period so as to determine whetherthe first cycle and the second cycle of the signal have thepredetermined frequency.

Still another embodiment of the invention comprises providing a firstavoidance zone transmitter; providing a second avoidance zonetransmitter; placing the first avoidance zone transmitter in a firsttransmission location; placing the second avoidance zone transmitter ina second transmission location; initiating transmission of a controlsignal from the first avoidance zone transmitter; initiatingtransmission of the control signal from the second avoidance zonetransmitter; varying the initiation of successive transmissions of thecontrol signal from the first avoidance zone transmitter withinsuccessive control signal windows.

According to another embodiment of the invention, a system is providedcomprising generating a control signal for transmission to an animalcontrol receiver, wherein the control signal is generated fortransmission within a control signal window and wherein the controlsignal window is longer than the control signal; determining a firstpoint in time within the control signal window to begin transmission ofthe control signal, wherein the first point in time within the controlsignal window allows for transmission of the control signal within thecontrol signal window; initiating transmission of the control signal atthe first point in time.

In accordance with another embodiment of the invention, a system isprovided comprising receiving a first control signal from an animalcontrol transmitter; initiating a routine for controlling at least onecorrection signal to the animal in response to the receiving the firstcontrol signal from the animal control transmitter; establishing acontrol signal window for receipt of a second control signal from theanimal control transmitter; checking for the second control signalwithin the control signal window so as to allow the second controlsignal to be transmitted at a different initiation point relative to thecontrol signal window from the initiation point of the first controlsignal.

In yet another embodiment of the invention, a system is providedcomprising providing a transmitter; storing one of a plurality ofidentifiers with the transmitter wherein each of the plurality ofidentifiers is associated with a corresponding animal; transmitting fromthe transmitter an animal control signal matching the selectedidentifier without receiving via an animal control receiver a signal toindicate to the transmitter the presence of the animal in the targetzone.

Still another embodiment of the invention comprises receiving an animalcontrol signal from a transmitter, wherein the animal control signal isreceived without the receiver transmitting a signal to indicate to thetransmitter the presence of the animal in a target zone; storing anidentifier in a memory, wherein the identifier is associated with one ofa plurality of animals; providing a processor configured to initiate aroutine for application of the correction signal to the animal if theanimal control signal received from the transmitter matches theidentifier.

Yet another embodiment of the invention comprises detecting atransmitted signal with a detector indicating the detector is locatedwithin a first zone; applying a first sequence of correction signals forcontrolling the animal; determining whether the animal has not movedfrom the first zone after the applying the first sequence of correctionsignals; waiting a period of time after the applying the first sequenceof correction signals; in response to the determining that the animalhas not moved from the first zone after the period of time, applying asecond sequence of correction signals for controlling the animaldifferent from the first sequence of correction signals.

Further embodiments will be apparent from the specification andaccompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a plan view of a home utilizing avoidance zones,according to one embodiment of the invention.

FIG. 2 illustrates a signaling format for communicating between atransmitter and a receiver, according to one embodiment of theinvention.

FIG. 3 illustrates an animal collar according to one embodiment of theinvention.

FIGS. 4A and 4B illustrate a flowchart demonstrating a method oftransmitting a signal for controlling an animal according to oneembodiment of the invention.

FIG. 5 illustrates a flowchart demonstrating a method of receiving asignal for use in controlling an animal according to one embodiment ofthe invention.

FIG. 6 illustrates a flowchart demonstrating a method of transmitting alow power signal for use in controlling an animal according to oneembodiment of the invention.

FIGS. 7A and 7B illustrate a flowchart demonstrating a method ofreceiving a signal for use in controlling an animal, according to oneembodiment of the invention.

FIG. 8 illustrates a method of modulating a signal so as to produce atrain of signals, according to one embodiment of the invention.

FIG. 9 illustrates a transmitting and receiving system for controllingan animal, according to one embodiment of the invention.

FIGS. 10A and 10B illustrate a flowchart demonstrating a method ofcombining more than one transmitters to create a zone for controlling apet, according to one embodiment of the invention.

FIGS. 11A and 11B illustrate a flowchart demonstrating a method ofaltering the initiation of a transmission within a window of time,according to one embodiment of the invention.

FIGS. 12A and 12B illustrate a flowchart demonstrating a method ofreceiving a signal occurring at different initiation points withinwindows of time, according to one embodiment of the invention.

FIG. 13 illustrates a repeated signal shown as occurring at differentinitiation points within repeated windows of time, according to oneembodiment of the invention.

FIG. 14 illustrates a system for transmitting and receiving an animalcontrol system, according to one embodiment of the invention.

FIG. 15 illustrates a flowchart demonstrating a method of utilizingmultiple animal identifiers, according to one embodiment of theinvention.

FIG. 16 illustrates a flowchart demonstrating a method of receiving ananimal control signal identifying one of many correction signals forapplication to the animal, according to one embodiment of the invention.

FIG. 17 illustrates a system for transmitting and receiving animalcontrol signals, according to one embodiment of the invention.

FIGS. 18A and 18B illustrate a flowchart demonstrating a method ofapplying a correction signal to an animal, according to one embodimentof the invention.

FIG. 19 illustrates the block diagram of a system for applying acorrection signal to an animal, according to one embodiment of theinvention.

FIG. 20 illustrates a graph of a correction signal that can be appliedto an animal according to one embodiment of the invention.

FIG. 21 illustrates how avoidance zones can be established around atransmitter, according to one embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary layout of a home in which some of theembodiments of the invention can be used. For example, FIG. 1 showstransmitters 10 and 12 being placed at the ends of a long couch 16. Onemight desire to keep pets off a couch. However, for couches placed inthe middle of the room or along a wall with few AC outlets, it isdifficult to conveniently power the transmitters. Similarly, FIG. 1shows a transmitter 30 placed near a toilet 34 so as to discourage petsfrom drinking out of a toilet. Again, AC outlets are not typicallyconveniently located in bathrooms. Furthermore, running power cords in abathroom can be dangerous due to the shock hazard. As another exampletransmitter 40 is placed near a front door in FIG. 1 to keep house petsfrom running out the door when opened or possibly for keeping dogs fromjumping on visitors when they enter the home. Again, the front door areaof a home is often one that does not have an AC outlet for providing apower source for the transmitter.

Thus, a battery powered transmitter is necessary in these and othersituations. Providing a battery powered transmitter that provides asignal that is of sufficient strength so that it can create a zone ofprotection has been difficult to achieve until now. While AC units arecapable of providing a strong signal with little worry about the powerbeing used to transmit the signal, battery powered units need to be ableto generate a signal of sufficient strength while at the same timeallowing the signal to be transmitted for several months. This will keepthe pet owner from having to change the batteries too frequently.According to one embodiment of the invention, it would be desirable notto have to change a unit powered with 3 “AA” cell batteries for a periodof six months. According to other embodiments of the invention, atransmitter that could transmit a signal for 6, 5, 4, or 3 monthswithout requiring replacement of the batteries would be sufficient.

In addition to showing that the transmitters in FIG. 1 are capable ofbeing battery powered, FIG. 1 also shows that the transmitters can beused together to form a large avoidance zone. Namely, FIG. 1 shows thattransmitters 10 and 12 can be used together to form an avoidance zonethat covers the entire couch 16. This is beneficial in that it allows alarge area to be covered with a transmitter/receiver system. While FIG.1 shows that the avoidance zone is created by units placed at the endsof the couch, one could also place the units underneath the couch toshorten the avoidance zone.

FIG. 1 also shows that different animals can be kept away from differentareas. For example, the dashed line signals around transmitter 30 and 40are intended in this example to correct a dog that might drink from thetoilet or run out through the open front door. The signal around couch16 is intended to correct a cat that might like to scratch or climb onthe couch. Regardless of the reason behind placing a transmitter in alocation, FIG. 1 illustrates that different animals can enter differentavoidance zones that are not programmed to apply to them, while theother animals for which the avoidance zone was designed are kept awayfrom the avoidance zones.

As noted above, the ability to keep pets out of certain areas of thehome requires that a battery powered unit be used in order to place atransmitter in an effective location. As a result, the unit needs to beof sufficiently low power so that it can last for a dependably longenough time, e.g., around 3 to 6 months, so as not to be annoying to theconsumer who has to replace the batteries.

To accomplish a low power transmitter, the signal shown in FIG. 2 can beused. FIG. 2 illustrates that a header signal is used to wake up areceiver. In this example, the header signal is shown as being 16 cyclesof the carrier wave. This header is sensed by the receiver which detectsthe presence of energy. A buffer period of eight cycles is shown in FIG.2 to separate the header and payload of the data signal. The bufferperiod can be used to allow the receiver to initialize after being wokenup by reception of the header signal. The transmitter then transmits thepayload signal which, according to this example, is comprised of 8 datasegments. Each of the data segments is transmitted for 8 cycles so as toallow the receiver to determine the value of the data segment. Thus, thetransmitter, according to this example can transmit 8 data bits.

To reduce the power requirements of the transmitter, a uniquetransmission scheme can be used to reduce the number of transmissionsthat draw current from the power source. The signals that draw currentfrom the power source are the ones that reduce the life of the batterysource. For example, a data signal for each data bit in FIG. 2 can betransmitted only when a binary data bit of the value “1” occurs. Thisallows the transmitter to conserve power by not transmitting a signal,where the lack of transmission during a specific time period indicatesto a receiver a binary data bit of the value “0”.

This transmission scheme can be illustrated by flowchart 400 in FIGS. 4a and 4 b. In block 410 of flowchart 400, a digital message is providedfor communication to a receiver. An example of this is the code“10100000” which can be associated with the message that a correctionsignal should be applied to a large dog wearing the animal collarprogrammed with that code. In block 420, the digital message is storedat the transmitter for transmission. A carrier wave, such as a generallysinusoidal wave at 6.25 KHz is provided for use by a transmitter (block440). The transmitter can then transmit the carrier wave in accordancewith the digital message so as to transmit the carrier wave for eachoccurrence of a first digital signal (e.g., a digital “1”) and not totransmit the carrier wave for each occurrence of the opposing digitalsignal or second digital signal (e.g., a digital “0”). Thus, for thedigital payload in FIG. 2 of “10100000”, a series of 8 cycles of thecarrier wave would be applied, followed by 8 cycles of no transmissionof the carrier wave, followed by transmission of another 8 cycles of thecarrier wave, followed by no transmission of the carrier wave for yetanother 40 cycles. The receiver could then detect what digital messagewas being conveyed based on the occurrence or lack of occurrence of thecarrier wave after the wake up signal.

As shown in block 460, a battery operated unit could be used to transmitthis signal since it requires very little power. However, where atransmitter unit is configured with both a battery power mode and an ACpower mode, then the AC power mode could transmit in this fashion, aswell. It is envisioned that this transmission scheme will be verybeneficial when used as a battery powered transmission scheme, however.

Block 470 illustrates that the carrier wave signal is repeatedlytransmitted according to the digital message. This allows the receiverassembly worn by the animal to trigger off of the received signal andapply the appropriate correction signal. Thus, for example, the encodedcarrier wave signal can be sent repeatedly every 300 ms to convey the 8bit message. If the animal wearing a collar assembly receiver isstanding within an avoidance zone, it can be issued a correction signalevery time the 8 bit signal is received.

This reception scheme is illustrated further by flowchart 500 in FIG. 5.In block 510 of FIG. 5, the wake up signal is received by the animalcollar receiver to alert the receiver of an incoming message, i.e., thepayload in the example of FIG. 2. Thus, a receiver is provided in block520, such as by fastening an animal collar receiver around the neck of apet. FIG. 3 illustrates an exemplary animal collar assembly 300. Inblock 530 a carrier wave signal is received for use in controlling ananimal. As explained above, this can involve receiving a series ofcycles of a substantially sinusoidal waveform transmitted by thetransmitter. The message communicated by the carrier wave signal can beused to control the animal.

In block 530, the digital message is determined from the carrier wavesignal, wherein reception of the carrier wave corresponds to a firstdigital signal in the digital message and non-reception of the carrierwave corresponds to a second digital signal in the digital message. Thesecond digital signal is the opposite of the first digital signal.Therefore, if the first digital signal is a “1” then the second digitalsignal is a “0” and vice versa. Once the digital message is determinedfrom the carrier wave signal, then the digital message can be used todecide whether to apply a correction signal, e.g., in the form of asound or a stimulation signal. According to one example, the digitalmessage can be associated with a specific animal collar. Any animalcollar that is programmed with that digital message and receives thatdigital message would know to apply a correction signal to the pet. Anyanimal collar not pre-programmed with that digital message and whichreceived that digital message would conclude not to apply the correctionsignal. Thus, different pets could be controlled by differenttransmitters—thus keeping cats away from a sofa that they might scratch,while allowing dogs to sleep at the side of the sofa. As anotherexample, the digital message could be indicative of a level ofstimulation to apply. Thus, for a house full of big dogs that have atendency to both get in the trash can in the kitchen as well as run outthe front door, a digital signal sent by the transmitter at the trashcan could be equated with a weak correction signal while the digitalmessage sent by the transmitter at the front door could be equated witha strong correction signal (since you would want to prevent the dogsfrom running out the front door and into the traffic). A table look upfunction in a processor could be used to determine what correctionsignal to apply for each digital message received. Furthermore, acombination of these examples could be used.

FIG. 8 illustrates an example of the transmission scheme discussedabove. Namely, in FIG. 8 a digital signal 800 is used to modulate asubstantially sinusoidal carrier wave 804. While a substantiallysinusoidal carrier wave is used for exemplary purposes, other signalsmight be useful in some situations. The carrier wave is modulatedaccording to the digital input to produce the sequence of carrier wavesshown in graph 808. These signals are transmitted to the receiver fromthe portable transmitter in FIG. 1, for example. In this example, ascompared to FIG. 2, the carrier wave is only transmitted for 3 cycleswhen a digital “1” is encountered. Each occurrence of a digital “0” inthe digital input produces a “silent” period of no transmission of thecarrier wave 804.

It should be understood that for purposes of this patent, a carrier waveis considered to be the signal that is transmitted from the transmitterto the receiver for use in communicating a message. In some instances,transmission of a carrier wave will be interrupted for purposes ofconveying the message. Furthermore, in some instances, the carrier wavewill have the same general shape as the input wave form. Furthermore,for purposes of this patent, it should be understood that a pattern ofsignals has a beginning signal and an ending signal.

This on/off modulation scheme is beneficial from a power perspective inthat it reduces the number of current drawing instances whencommunicating a digital message. In a pulse width modulated system, thewidth of a transmission indicates the value as being a “1” or a “0”.Thus, pulse width modulation draws current regardless of whether a “1”or a “0” is transmitted. The on/off scheme avoids drawing current for atleast one of the signals (i.e., either the 1's or the 0's). FIG. 8 is anexample in which no current is used to convey the 0's. As explainedbelow, this scheme can be utilized further by selecting a coding schemefor the digital message that reduces the number of times that thecurrent drawing value occurs in the message (e.g., reducing theoccurrence of “1's” to only twice in an 8 bit message so as to convey apredetermined message).

FIG. 9 illustrates a transmitter/receiver system that can be used forimplementing the scheme described above. In FIG. 9, a transmitter system900 is configured to transmit a carrier wave signal, such as that shownin FIG. 8 to receiver system 950. The transmitter 900 is shown as havinga memory 908, a power supply 912, a signal generator 924, a modulator920, and a transmitter 916. These elements can be configured byindependent circuits or in some instances with the use of a processor.The memory, for example, could be configured from a series of switchesto store the digital message transmitted by the transmitter system 900.Alternatively, the memory could be configured from a processor that haslocal memory in which the digital message is stored. Alternatively, aseparate memory device could be used to store the digital message. Thesignal generator 924 can be used to generate a substantially sinusoidalsignal for modulation by the digital message and transmission to thereceiver system 950. The signal generator and memory are coupled withthe modulator circuit 920 to allow the digital message to be used tomodulate the signal generated by the signal generator. Again, aprocessor could be used to accomplish the modulation. The modulatorcould be a separate circuit or integral with the transmitter 916. Thus,the transmitter can be coupled with the memory and the generator so asto transmit the carrier wave in accordance with each occurrence of thefirst digital signal and so as not to transmit the carrier wave inaccordance with each occurrence of the second digital signal in thedigital message. The power supply is shown as block 912. The powersupply used for the on/off transmission scheme described above can beeither battery powered or AC powered. However, it is envisioned that inmany instances a battery powered system will provide a great deal offlexibility for the user in placing the transmitter in locations whereno AC power is readily available.

The receiver system 950 is shown having a receiver 958, a processor 962,a wake up circuit 954, a sound generator 970 and a stimulation generator966. The receiver is configured to receive the carrier wave signal sentby the transmitter. As explained above, the digital message embodied bythat carrier wave can be used to determine how to control an animal suchas one's pet dog or cat. The receiver is coupled with the processor 962to translate or demodulate the carrier signal. Thus, the processor isconfigured to determine a digital message from the carrier wave signalwherein reception of the carrier wave corresponds to a first digitalsignal (e.g., a “1”) in the digital message and non-reception of thecarrier wave corresponds to a second digital signal (e.g., a “0”) in thedigital message. The first and second digital signals are opposites ofone another (e.g., “1” and “0” or “0” and “1”). FIG. 9 shows alternativecorrection signal generators that can be used to generate the correctionsignal sent to the animal. In FIG. 9, a sound generator 970 is shown forgenerating an audible sound within the hearing range of the animal. Thevoltage generator 966 can also be used to generate a stimulation signalfor the animal. Again, as shown in FIG. 3, the receiver system can bepart of a collar assembly 300 for coupling with the animal. A wake upcircuit 954 is also shown in FIG. 9. The wake up circuit is a low powercircuit that allows the receiver system to sense the presence of anenergy signal, such as an RF signal. The wake up circuit can be operatedto sense the signal while the remaining circuit elements are run in lowpower or sleep mode. This allows the receiving system to be operated atlow power until needed. Upon sensing a signal, such as the header signalshown in FIG. 2, the remaining circuit elements in receiver system 950can be invoked as needed.

As noted earlier, the use of a transmitter is limited by the lifetime ofthe transmitter's power supply. Thus, a highly beneficial transmitter isone that can provide a sufficiently powerful signal so as to be receivedby the receiver while at the same time enduring for a long period oftime without requiring a change of batteries, such as for 3, 4, 5, or 6months. This allows the transmitter to be portable so that it can beused in locations that do not have AC power readily available. It alsoallows for the transmitter to be operated for substantially long periodsof time without the pet owner having to change the batteries. A methodof implementing such a low power transmitter can be seen in flowchart600 in FIG. 6. According to FIG. 6, a transmitter is provided in block610 and power is provided for the transmitter in block 620. A messagefor communication is provided in block 630 for communication to areceiver, wherein the message is configured to implement a routine forapplication of a specific correction signal to the animal. In block 640,the message is transmitted at about 0.0167 Watts average power.According to another embodiment, the message could be transmitted at0.00333 Watts average power. According to yet another embodiment of theinvention, the message could be transmitted at 0.00167 Watts averagepower; thus, allowing the transmitter to be operated with 3 “AA” cellbatteries. As shown in block 660, the message can be repeatedlytransmitted to the receiver.

To implement such a low power system, the signaling format shown in FIG.2 can be used according to the transmission scheme described in FIGS. 4a and 4 b. Similarly, the transmitter system 900 in FIG. 9 can be usedto transmit the low power system signal. For example, a payload signalsent according to the formatting of FIG. 2 can be sent where the payloadsignal comprises only 2 digital “1” values and 6 digital “0” values.This allows 21 distinct messages to be sent with an 8 bit message.Furthermore, as shown in FIG. 2, the transmitter can be configured toonly transmit the carrier wave for occurrences of digital “1's” whereineach digital one causes the carrier wave to be transmitted for 8 cycleseach of the carrier wave at 6.25 KHz. For this example, an average poweris measured to be only 0.00165 Watts or 370 microamps at 4.5 V. This isa significant improvement over the power needed by some AC powered pulsewidth modulated devices, such as the IFA-12 which at maximum outputrequires approximately 115 mA at 14.3 V which is 1.65 Watts. As can beseen, the average power for the AC unit is 1000 times that of thisembodiment of the invention.

A receiver can be used to detect the digital message sent by thetransmitter in a unique fashion. This is illustrated, for example, byflowchart 700 in FIGS. 7 a and 7 b. In block 710, a receiver isconfigured to receive a signal having a predetermined frequency. Forexample, for a carrier wave being transmitted at 6.25 KHz, thepredetermined frequency would be 6.25 KHz. To conserve power, thereceiver can be configured with a wake up detector circuit to sense thepresence of an RF signal for example. The wake up signal can be thatshown in FIG. 2 for example—a series of cycles of the carrier wave for16 cycles followed by 8 cycles of no transmission of the signal.

To determine that the transmission that is being received is of thepredetermined frequency, the receiver can apply a unique method tocalculate the frequency. Namely, the receiver can sample the receivedsignal according to the following formula:Peak_(—) Sig=(a0°−a180°)²+(a90°a270°)² wherein “a” is the value of thesignal at each expected phase position.By sampling the signal at every 90 degree location for an expectedfrequency, two successive cycles of the received waveform should havethe same Peak_Sig value. If the Peak_Sig values for the successivecycles do not have the same value, then one can determine that thesignal being received is not being transmitted at the predeterminedfrequency.

Alternatively, one could configure the system to wake up if any signalis received. Thus, one could wait until the payload signal was receivedbefore determining whether the payload signal was being transmitted atthe predetermined frequency.

Thus, as shown in block 720, the receiver can detect not only thepresence of a signal but can also make a determination that the signalthat is being received is of the predetermined frequency that thereceiver is configured for. If the signal is detected to be of thepredetermined frequency, then the receiving circuit elements can beinitiated to receive the transmission packet message. This can beimplemented according to one embodiment of the invention by taking afirst set of samples of the signal at multiple intervals during a firsttime period corresponding to at least one cycle at the predeterminedfrequency, as shown in block 730. Then, this first set of samples can beused to calculate a characteristic of the signal for the first cycle, asshown in block 740. Then, a second set of samples of the signal can betaken at multiple intervals during a subsequent time periodcorresponding to at least one cycle at the frequency. In block 755, thesecond set of samples is utilized to calculate the characteristic of thesignal during the second cycle, for example. The calculatedcharacteristic of the first time period (e.g., cycle #1) can be comparedwith the calculated characteristic of the subsequent time period (e.g.,cycle #2) so as to determine whether the first cycle and the secondcycle of the signal have the same value and thus were sent at thepredetermined frequency. If so, the digital message embodied in thetransmission packet can be determined from the signal, as shown in block770. Once the digital message is determined, it can be used to triggerapplication of the correction signal that is transmitted to the animal,as shown in block 780.

As shown in block 790, one such characteristic that can be determined isthe Peak_Sig according to the formula shown above. The Peak_Sig can thenbe computed for each of the 8 cycles per bit, as shown for FIG. 2. Thus,if desired, this allows a processor to compare the Peak_Sig value foreach cycle. However, one could even choose to skip a cycle, rather thancalculating Peak_Sig for every cycle. If the Peak_Sig values for the 8cycles match, then they confirm that the signal is being transmitted atthe predetermined frequency—i.e., at 6.25 KHz according to this example.Furthermore, if the transmitter/receiver scheme utilizes the codingsystem that only two of the 8 bits will be a digital “1” and only “1's”will cause a carrier wave to be transmitted, then the receiver candetermine that the received signal corresponds to a digital “1”.Similarly, the Peak_Sig can be applied to the time interval associatedwith the second most significant bit in FIG. 2. If no signal is receivedduring this time interval, then the receiver will associate the lack ofreception of a signal with a digital “0” under this example. It shouldbe noted that the transmission scheme could be reversed so that thereceiver recognized “no-reception of the carrier wave” as a “1” insteadof a “0” and “reception of the carrier wave” as a “0” instead of a “1”.

To implement the method of FIGS. 7 a and 7 b, the receiver shown in FIG.9 could again be used. The receiver could be configured to receive thesignal having the predetermined frequency, such as 6.25 KHz.Furthermore, the processor 962 could be configured to take the first setof samples with the receiver at multiple intervals during the first timeperiod corresponding to at least one cycle at the frequency. Theprocessor could be configured to calculate the characteristic for thesamples, such as by calculating the Peak_Sig value described above. Theprocessor could then repeat this process for a subsequent cycle.Similarly, the processor could be configured to compare thecharacteristics for the two cycles to see if they are equivalent andindicative that the transmission is at the predetermined frequency.Furthermore, the processor can be configured to determine from thereceived transmission packet the digital message. From the digitalmessage, the processor can determine whether to transmit a correctionsignal to the animal. One way to implement this would be to store adigital message in the processor, thus designating that receiver as onethat would initiate a correction signal every time the digital messageis received. Then, the processor could merely compare the receiveddigital message with the value stored at the processor. If they match,the correction signal can be applied. If they don't match, then thereceiver would not apply a correction signal.

The coding scheme used in the example above is beneficial because itreduces the need for power, as well. Namely, the coding scheme providesthat for every eight bit packet, only 2 of the bits will be 1's. Thus,21 codes can be communicated to the receiver by only transmitting for 2data bits during the payload portion of the signal. As can beappreciated by one of ordinary skill in the art, additional messagesbeyond the 21 could be provided by lengthening the payload to a numbergreater than 8 bits, e.g., 16 bits where only two of the bits are “1”.By only having to transmit two bits, the power requirements are kept lowunder this coding scheme, as opposed to a transmission scheme in whichmore than two bits had to be transmitted on average per 8 bit message orone in which a signal had to be transmitted regardless of whether a “1”or a “0” was being transmitted.

As shown in FIG. 1, one embodiment allows for multiple transmitters tobe used in conjunction with one another. This can be accomplished by themethod illustrated by flowchart 1000 in FIGS. 10 a and 10 b. First, onecan provide a first avoidance zone transmitter as shown in block 1004.Then, one can provide a second transmitter as shown in block 1008. Thetransmitter can be placed in their respective locations within a house,for example, as illustrated by blocks 1012 and 1016. Then, atransmission of a control signal can be initiated from the firsttransmitter as shown in block 1020 as well as from the secondtransmitter. To keep the two transmitters from interfering with oneanother, the transmission of their signals can be varied. Thus, as shownby block 1024, the initiation of successive transmissions of the controlsignal from the first transmitter can be varied within its transmissionwindows or control signal windows. Similarly, the initiation of thetransmission packets sent by the second transmitter can be varied aswell within its transmission windows, as shown by block 1028. As aresult, there will be less of a likelihood that the two transmitterswill transmit the control signal at the same time and createinterference for one another. For example, FIG. 1 illustrates that twotransmitters can be placed at the opposite ends of a couch to establisha large avoidance zone for the couch—for example to keep a cat off ofthe couch when the owner is out of the room. The two transmitters can beconfigured to transmit at varying intervals so that there is lesslikelihood that the signals from one another would interfere with eachother. Thus, instead of only being able to protect part of the couchwith one transmitter or ineffectively protect the couch with twotransmitters that do not vary their transmission points, the systemdescribed above can be used to effectively protect a large area.

FIGS. 11 a and 11 b further illustrate the method of varying the time ina sequence of transmission windows. FIG. 13 and FIG. 2 help toillustrate the method of flowchart 1100, as well. FIG. 2 illustrates awake up signal and data packet that are sent as a transmission packet toa receiver. This transmission packet corresponds to the hatched areawithin the transmission windows “T” shown in FIG. 13. For a 6.25 KHzcarrier signal, for example, the period of the carrier signal is 160microseconds per cycle. To transmit a transmission packet according theexemplary scheme shown in FIG. 2 would take 88 cycles at 160microseconds per cycle. Thus, this is equal to 14.08 milliseconds totransmit the entire transmission packet. A transmitter can transmit thetransmission packet within successive windows (e.g., transmissionwindows “T” in FIG. 13) at 300 milliseconds and be very effective. Ofcourse, other time periods could be used as well. Thus, when 300millisecond windows are used, there is quite a bit of room for varyingwhen to start transmission of the 14.08 millisecond transmission packet.FIG. 13 shows the initiation point varying from window to window frompoints “A” to “B” to “C” and back to “A” again. To accomplish thisvariation, one can use a randomization circuit, such as a processorconfigured to generate a random number or a separate circuit to generatea randomization factor, and then choose the initiation point (i.e., “A”,“B”, “C”, etc.) within each window. This results in the packet beingsent within every window—but, it does not require that the packet besent at the same initiation point within every window. As a result, thisjitter helps prevent two units that are being used in close proximitywith one another from interfering with one another—or at leastsignificantly reduces the chance that a frequent interference wouldoccur.

FIGS. 11 a and 11 b illustrate a transmission scheme according toflowchart 1100. In block 1104, a control signal is generated fortransmission to an animal control receiver, wherein the control signalis generated for transmission within a control signal window and whereinthe control signal window is longer than the control signal. In block1108, a first point within the control signal window is determined fromwhich to begin transmission of the control signal. The first point isselected so as to still allow for transmission of the control signalpacket within the control signal window. In block 1112, transmission ofthe control signal at the initiation point is initiated. In block 1116,the control signal is generated for transmission to the animal controlreceiver within a second control signal window having the same period asthe first control signal window. A second point in time or initiationpoint is determined for the second control signal window from which tobegin transmission of the control signal, as shown in block 1120. Thesecond initiation point allows for the transmission of the controlsignal packet within the second control signal window. Then, thetransmission of the control signal can be initiated again starting atthe second initiation point, as shown in block 1124. This process can berepeated by transmitting the control signal packet in successive controlsignal windows of the same period while varying the initiation oftransmission of the control signal packet within successive controlsignal windows.

To implement the variation of the initiation point within control signalwindows, one can use a randomization circuit to select successiveinitiation points. However, in some instances, one might also use apredetermined pattern to accomplish the variation. Thus, for example, aprocessor might choose to randomize the initiation point for 4 out of 5transmission windows—but, initiate the transmission for the fifth windowat the beginning of the fifth transmission window.

A receiver that receives this “jittered” type of signal can beconfigured to check for the variation. For example, the flowchart 1200shown in FIGS. 12 a and 12 b illustrate one such method. In block 1204of flowchart 1200, a first control signal is received from an animalcontrol transmitter. A routine is initiated for controlling at least onecorrection signal to the animal in response to receiving the firstcontrol signal from the animal control transmitter, as shown in block1208. A control signal window can be established for receipt of a secondcontrol signal from the animal control transmitter in block 1212.Furthermore, a check can be made for a second control signal within thesecond control signal window so as to allow the second control signal tobe transmitted at a different initiation point in the second controlsignal window than was used for the initiation point for the controlsignal in the first control signal window, as shown in block 1216. Thereceiver can terminate the correction signal routine if the secondcontrol signal is not received within the second control signal window,as shown by block 1220. However, if the second control signal isreceived within the second control signal window, as shown by block1224, then the routine for applying the correction signal can continue.Thus, in this example, block 1228 illustrates that the correction signalis applied to the animal.

According to one correction signal routine, a series of correctionsignals can be applied to the animal for every correction signal windowin which the control signal packet is received. The initial magnitude ofthe correction signal that is applied to the animal can be determined inone example by determining the strength of the received signal. Thus,the strength of the signal can be used to indicate the relative locationof the animal within the avoidance zone, i.e., a strong signal indicatesthe animal is closer to the transmitter than would a weak signal.Furthermore, according to the routine shown in block 1232, a eachsubsequent correction signal that is applied to the animal during itstime inside the avoidance zone is applied with a greater intensityrelative to the previous correction signal—up to a predetermined maximumintensity. After a predetermined time at the maximum intensity, the unitwould shut down. Similarly, block 1236 illustrates that after a periodof time in which the animal is not removed from the zone, the timeintervals between correction signals could be randomized. As notedearlier, a collar assembly can be used to hold the receiver and applythe correction signal in the form of a sound or an electricalstimulation, as shown in block 1240.

FIG. 14 shows a transmitter/receiver system to implement the method ofFIGS. 13 a and 13 b, according to one embodiment of the invention.Namely, FIG. 14 illustrates a system 1400 of transmission system 1410and receiving system 1450. The transmission system in this example isshown as having a memory 1414 for storing a control signal fortransmission to an animal control receiver. The memory could take avariety of forms. It could be a memory chip programmed with theinformation. Alternatively, it could be as simple as a series ofswitches such as BCD switches configured to store an 8 bit message, forexample. This would allow the transmission system to be configured to aparticular message depending on how the pet owner wanted to use thetransmitter—for example, for a cat, a little dog, a big dog, etc. FIG.14 also shows a transmission initiation circuit for varying theinitiation point for transmitting a control signal within a controlsignal window. In FIG. 14, the processor 1418 can be configured toselect and vary the initiation points within successive windows. Forexample, according to one embodiment, the processor can be configuredwith a randomization feature. FIG. 14 also shows a transmitter coupledwith the memory and coupled with the processor. The transmitter can beconfigured to transmit the control signal stored by the memory as partof a transmission packet within successive control signal windows atvarying points of initiation within successive control signal windows.As explained above, the processor can be further configured to vary theinitiation point by either randomizing the initiation point or applyinga predetermined sequence of initiation points.

The receiving system is shown in FIG. 14 as system 1450. It is shown ashaving a receiver 1466 for receiving the signal from the transmitter. Ittoo is shown having a processor 1454. Furthermore, the example in FIG.14 is shown with a voltage generator or supply 1458 and a soundgenerator 1462. The processor is configured for initiating a routine forcontrolling at least one correction signal for application to the animalin response to receiving the first control signal from the animalcontrol receiver. For example, this routine could simply be theapplication of the correction signal every time that the control signalpacket is received from the transmitter. Furthermore, the processor isconfigured for establishing a control signal window for receipt of asecond control signal from the animal control transmitter while at thesame time allowing the second control signal to be transmitted at adifferent initiation point within the second control signal window asopposed to the initiation point that was used for the first controlsignal window. The processor and receiving system can be furtherconfigured to implement the routines described in FIGS. 12 a and 12 b,for example.

Referring to FIG. 2, each 8 bit signal sent in the exemplary signal ofFIG. 2 can be associated with a unique pet. For example a digital valueof “10100000” can be associated with correcting the pet wearing theanimal collar programmed to that code—such as the family cat. Similarly,the digital value of “10010000” can be associated with correcting thepet wearing the animal collar programmed to that code—such as the familydog. Table 1 shows an example of 21 different codes that can beimplemented with an 8 bit code when only two of the bits are allowed tobe 1 and the two 1's must be separated by a 0. This is a useful codingsystem for low power transmissions as explained above. Thus, code “0”could be used to control the family cat for which a tone is generated tokeep the cat away from avoidance zone 1. Similarly, code “1” could beused to control a small dog for which the correction signal is anappropriate electrical stimulation signal to encourage the dog to stayout of avoidance zone 2. Similarly, code 3” in Table 1 could be used tocontrol a large dog for which the correction signal is used to encouragethe large dog to stay out of avoidance zone 3. Thus, by using a systemwith multiple codes, a transmitter can be set to control a particularanimal. This allows the small dog to enter zones 1 and 3—but not zone 2.

TABLE 1 Code Number 7 6 5 4 3 2 1 0  0 1 0 1 0 0 0 0 0  1 1 0 0 1 0 0 00  2 1 0 0 0 1 0 0 0  3 1 0 0 0 0 1 0 0  4 1 0 0 0 0 0 1 0  5 1 0 0 0 00 0 1  6 0 1 0 1 0 0 0 0  7 0 1 0 0 1 0 0 0  8 0 1 0 0 0 1 0 0  9 0 1 00 0 0 1 0 10 0 1 0 0 0 0 0 1 11 0 0 1 0 1 0 0 0 12 0 0 1 0 0 1 0 0 13 00 1 0 0 0 1 0 14 0 0 1 0 0 0 0 1 15 0 0 0 1 0 1 0 0 16 0 0 0 1 0 0 1 017 0 0 0 1 0 0 0 1 18 0 0 0 0 1 0 1 0 19 0 0 0 0 1 0 0 1 20 0 0 0 0 0 10 1

FIG. 15 illustrates a flowchart 1500 for implementing a method ofestablishing different zones that can be used to control different pets.In block 1510, a transmitter is provided. In block 1520, multipleidentifiers are stored with the transmitter wherein each of theidentifiers is associated with a different animal. Alternatively, justone identifier can be stored at the transmitter or a series of switchescan be provided to allow the transmitter to be set to the appropriatecode in Table 1, for example, as the user desires, as shown in block1530. The transmitter can then transmit the animal control signal whichmatches the selected identifier as shown in block 1540. The system issimple in that it does not require that a signal be received from theanimal indicating that the animal is present within the zone. Rather, itidentifies the animal through its code so that a specific avoidance zonecan be set for that animal without keeping other animals from that zone.One example of transmitting the signal is to transmit a header, such asa wake up signal, as shown in block 1550 and also transmit a payloadwhich comprises the control signal, such as an 8 bit code having onlytwo digital “1's”, as shown in block 1560.

The receiving method can be implemented according to the example shownin FIG. 16 and flowchart 1600. In block 1600 a receiver receives ananimal control signal from a transmitter. The animal control signal isreceived without the receiver transmitting a signal to indicate to thetransmitter the presence of the animal in an avoidance (or target) zone,as shown in block 1610. The receiver can be configured to store anidentifier in its memory. The identifier is used to identify the animalas one of many animals in a household, for example. A processor isprovided to and configured to initiate a routine for application of thecorrection signal to the animal if the animal control signal receivedfrom the transmitter matches the identifier, as shown in block 1630.Furthermore, a correction signal can be generated for use by thecorrection routine, in block 1640.

FIG. 17 illustrates a system for implementing the method described inFIGS. 15 and 16. Namely, FIG. 17 shows system 1700 having a transmissionsystem 1700. The example shows a processor 1720 coupled with memory 1730and transmitter circuit 1740. The memory can be a memory chip or aseries of switches capable of being configured to store a message.Similarly, the processor can be configured to implement the transmissionmethod illustrated in FIG. 15. The receiver system 1750 is shown ashaving receiver 1760 and memory 1770 as well as processor 1780 andcorrection signal generators 1790 and 1795. Again, the memory can take aform similar to that described for the transmitter. Also, the processorcan essentially be configured to implement the method described in FIG.16.

In some cases, an animal might acclimate to regular, periodicstimulation when the animal enters an avoidance zone. Thus, the animalwill linger in the avoidance zone rather than be discouraged from beingpresent in the avoidance zone. This might be especially true forstubborn animals. To solve this problem, a random stimulation patterncan be used. The random stimulation can be more annoying to the animalthan the regular, periodic stimulation, thus encouraging the animal tovacate the zone.

For example, FIG. 20 illustrates an example of the randomizationprinciple. In FIG. 20 a series of control signals are transmitted andreceived by the receiver. Over a period of time the receiver increasesthe stimulation up to a predetermined maximum. This is shown by theramping up and leveling off of the signal in FIG. 20. After time “t1”measured from when the first correction signal in the sequence was firstapplied, the collar assembly worn by the animal can randomize thecorrection signal. FIG. 20 shows a variety of ways in which therandomization can be implemented. For example, it can be implemented asdifferent time intervals between correction signals, differingmagnitudes of the correction signal, and different lengths of thecorrection signal. Of course, at time “t2” the receiver will cease anystimulation in case the animal is caught in the avoidance zone.

FIG. 21 illustrates that the magnitude of the initial correction signalcan vary depending on the strength of the received signal at thereceiver. For example, FIG. 21 shows an avoidance zone covering areas Aand B. The area C is outside the avoidance zone. If the animal entersthe avoidance zone quickly so as to end up in area A before a correctionsignal can be sent, the receiver can use a higher magnitude correctionsignal. On the other hand, if the animal is just inside area B, thesignal received by the receiver will be of lower strength. The receivercan recognize this fact and use a correction signal of lower magnitude.

FIGS. 18 a and 18 b illustrate an example of a method of randomizingcorrection signals with a receiver assembly. In block 1804 of flowchart1800, a transmitted signal is detected with a detector indicating thatthe detector is located within a first zone, such as an avoidance zone.In response, a first sequence of correction signals is applied forcontrolling an animal in block 1808. A determination is made as towhether the animal has been stimulated but not moved from the zone, inblock 1812. As noted above, a time period can be measured from when thefirst stimulation in the sequence of stimulation signals was applied tothe animal. Thus, as shown in block 1816, the receiver assembly can waita period of time after the application of the first sequence of controlsignals. If the animal has not left the avoidance zone and a sufficientperiod of time has elapsed, a second sequence of correction signals canbe applied to the animal. The second sequence will be different from thefirst sequence so as to encourage the animal to leave the avoidance zonein view of the fact that the animal has apparently become accustomed tothe first sequence. Thus, block 1824 shows that the receiver system canrandomly select the time intervals between correction signals in thesecond sequence of correction signals. Furthermore, the receiver couldalso be configured to randomly select a signal magnitude for thecorrection signal in the second sequence of correction signals, as shownby block 1828.

FIG. 19 illustrates a system for generating a random pattern ofstimulation signals. Namely, FIG. 19 shows a receiver assembly 1900 suchas an animal collar assembly having a collar for coupling the receiverwith the animal and a transducer for transmitting a signal to theanimal. A transmitted signal from a transmitter is shown as signal 1902.The presence of the signal can be detected and received by detector 1904and processed by processor 1908. The processor can then causeapplication of the correction signal through the use of the correctionsignal generator 1912. If the animal does not respond to the initialsequence of signals, random generator 1916 can be used to randomize thecorrection signal as explained above. The correction signal can beapplied with speaker 1914 or electrical stimulation 1920.

For further background on electronic transmitter and receiver systemsfor use with animals the following U.S. patents are hereby incorporatedby reference for all purposes: U.S. Pat. No. 5,435,271; U.S. Pat. No.5,533,469; U.S. Pat. No. 5,870,973; U.S. Pat. No. 4,967,695; U.S. Pat.No. 5,636,597; U.S. Pat. No. 6,431,122; U.S. Pat. No. 5,559,498; U.S.Pat. No. 5,799,618; U.S. Pat. No. 6,058,889; U.S. Pat. No. 5,923,254;U.S. Pat. No. 6,073,589; U.S. Pat. No. 5,911,198; and U.S. Pat. No.6,459,378.

While various embodiments of the invention have been described asmethods or apparatus for implementing the invention, it should beunderstood that the invention can be implemented through code coupled toa computer, e.g., code resident on a computer or accessible by thecomputer. For example, software could be utilized to implement many ofthe methods discussed above. Thus, in addition to embodiments where theinvention is accomplished by hardware, it is also noted that theseembodiments can be accomplished through the use of an article ofmanufacture comprised of a computer usable medium having a computerreadable program code embodied therein, which causes the enablement ofthe functions disclosed in this description. Therefore, it is desiredthat embodiments of the invention also be considered protected by thispatent in their program code means as well.

It is also envisioned that embodiments of the invention could beaccomplished as computer signals embodied in a carrier wave, as well assignals (e.g., electrical and optical) propagated through a transmissionmedium. Thus, the various information discussed above could be formattedin a structure, such as a data structure, and transmitted as anelectrical signal through a transmission medium or stored on a computerreadable medium.

It is also noted that many of the structures, materials, and actsrecited herein can be recited as means for performing a function orsteps for performing a function. Therefore, it should be understood thatsuch language is entitled to cover all such structures, materials, oracts disclosed within this specification and their equivalents,including the matter incorporated by reference.

It is thought that the apparatuses and methods of the embodiments of thepresent invention and its attendant advantages will be understood fromthis specification. While the above is a complete description ofspecific embodiments of the invention, the above description should notbe taken as limiting the scope of the invention as defined by theclaims.

1. A method of creating an avoidance zone, said method comprising: providing a first avoidance zone transmitter; providing a second avoidance zone transmitter; placing said first avoidance zone transmitter in a first transmission location; placing said second avoidance zone transmitter in a second transmission location; initiating transmission of a control signal from said first avoidance zone transmitter; initiating transmission of said control signal from said second avoidance zone transmitter; varying the initiation of successive transmissions of said control signal from said first avoidance zone transmitter within successive control signal windows.
 2. The method as described in claim 1 and further comprising: varying the initiation of successive transmissions of said control signal from said second avoidance zone transmitter within successive control signal windows. 